The present invention relates to a pulse motor control circuit for use in driving a pulse motor in synchronism with an external synchronization signal, in factory automation (FA) facilities or precise machining facilities.
Conventionally, in such a pulse motor which is driven in synchronism with an external synchronization signal, the pulse motor 1 is driven by directly inputting the external synchronization signal 6 to a pulse motor driver 2 so that the pulse motor is utilized synchronous motor, in which the revolution speed proportional to a pulse frequency can be obtained, as shown in FIG. 5.
However, the pulse motor has characteristics as illustrated in FIG. 4. Namely, when the pulse frequency is within a self-start range, the pulse motor can be started in synchronism with the pulse frequency. However, when the frequency is increased, the pulse motor steps out and can not start at a frequency exceeding a certain frequency. This frequency is called a maximum self-start frequency. The frequency range exceeding the maximum self-start frequency is called the through range. The pulse motor cannot be started by a pulse signal having a frequency in this through range.
Accordingly, the conventional pulse motor control circuit encounters a problem that stepping out of the pulse motor is caused when the external synchronization pulse signal has a pulse frequency in the through range and the pulse motor can not be started.